I had a similar upbringing, being the "spare part" of an otherwise functional family.

I eventually went to a trusted friends place for a few weeks to clear my head, and allow time for me to be away from the environment that was causing me upset and hurt.

Amazingly a couple of weeks later I met up with my adoptive parents, with a support worker in tow and talked through everything.

In short, they thought I disliked, hated and did not want to communicate with them.. they did not realise what "trauma" meant on the introduction pack... Surprisingly it actually went better after that.

It's not the definite answer to your specific problem, but it may go some way to helping you.